1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to an LCD device having a double reduced data (DRD) pixel structure for enhancing an aperture ratio.
2. Discussion of the Related Art
In LCD devices, two substrates in which electric field generating electrodes are formed are disposed so that surfaces with the electrodes formed thereon face each other, liquid crystal molecules are injected between the two substrates, a voltage is applied to the electrodes, the liquid crystal molecules are driven by an electric field generated with the voltage, and an image is displayed based on a light transmittance which is changed according to movements of the liquid crystal molecules.
In the LCD devices, a twisted nematic (TN) mode or an in-plane switching (IPS) mode which is a driving mode of each of the LCD devices is determined depending on positions of a common electrode and pixel electrode of a liquid crystal panel. In particular, the IPS mode, in which the common electrode and the pixel electrode are arranged in parallel on one substrate to generate a lateral electric field, has a broader viewing angle than the TN mode that generates a vertical electrical field.
Recently, an advanced high-IPS (AH-IPS) mode which is improved from the IPS mode and increases luminance has been proposed. In the AH-IPS mode, the common electrode and the pixel electrode are alternately arranged on different layers on one substrate to generate a fringe field, thereby realizing improved image-quality characteristic over that of the IPS mode.
The LCD devices include a liquid crystal panel, a gate driving circuit for driving a plurality of gate lines which are formed in the liquid crystal panel, and a data driving circuit for driving a plurality of data lines which are formed in the liquid crystal panel. As sizes of the LCD devices are enlarged and a resolution becomes higher, the number of driving circuits increases.
However, since the data driving circuit is relatively more expensive than other elements, research and development are done on technology for reducing the number of driving circuits so as to reduce the manufacturing cost of each LCD device. As an example of the technology, a double rate driving (DDR) structure has been proposed. In the DDR structure, although the number of gate lines increase by two times, the number of data lines decreases by half (½), and thus, the number of driving circuits decreases by half, and a resolution is maintained.
Hereinafter, a related art LCD device having a DRD pixel structure will be described with reference to FIGS. 1 to 3.
FIG. 1 is an equivalent circuit of the related art LCD device having the DRD pixel structure, and FIG. 2 is a plan view of the related art LCD device having the DRD pixel structure.
Referring to FIGS. 1 and 2, the related art LCD device having the DRD pixel structure includes two gate lines GL1 and GL2 which are formed on a substrate, a data line DL which is formed to cross the gate lines GL1 and GL2, and a common electrode line CL which is formed between adjacent data lines DL to cross the gate lines GL1 and GL2.
A plurality of pixels P1 and P2 are defined by the gate lines GL1 and GL2, the data line DL, and the common electrode line CL.
Each of the plurality of pixels P1 and P2 is coupled to the gate lines GL1 and GL2 and one data line DL.
In this case, first and second thin film transistors (TFTs) Tr1 and Tr2 which are coupled to the two gate lines GL1 and GL2 and the one data line DL are formed outside the two gate lines GL1 and GL2, which are formed in an alternating pattern.
In detail, the first and second TFTs Tr1 and Tr2 are disposed outside the gate lines GL1 and GL2, which are formed to be separated from each other and define pixel areas P1 and P2. The first TFT Tr1 is coupled to a first gate line GL1 and a first pixel P1, and the second TFT Tr2 is coupled to a second gate line GL2 and a second pixel P2.
A first contact hole CH1, which connects the common electrode line CL and a common electrode (not shown), is formed between the gate lines GL1 and GL2 which are alternately formed. A second contact hole CH2, which connects the first and second TFTs Tr1 and Tr2 to a pixel electrode PX, is formed outside the gate lines GL1 and GL2 which are alternately formed.
In this case, in order to reduce light leaking around the first and second contact holes CH1 and CH2, a black matrix BM having a certain length D is formed on an upper substrate (not shown) which is provided to face the substrate.
FIG. 3 is a cross-sectional view of the LCD device of FIG. 2, and is a view illustrating light leakage which occurs around the second contact hole CH2.
Referring to FIG. 3, the related art LCD device includes an active layer 13, a drain electrode 14b, a protective layer 16 including the second contact hole CH2 which exposes the drain electrode 14b, a common electrode CX, an insulation layer 17 including the second contact hole CH2, a pixel electrode PX which is coupled to the drain electrode 14b through the second contact hole CH2, and an alignment layer P1, which are sequentially formed on a substrate 10.
In this case, the alignment layer P1 flows down to the second contact hole CH2 due to a flowability of the material forming the alignment layer P1, and is non-uniformly formed around the second contact hole CH2 (see a circular block S). For this reason, light leakage occurs. To prevent the light leakage, the black matrix BM having the certain length D is formed on an upper substrate 20 which is provided to face the substrate 10.
In the related art LCD device having the DRD pixel structure, the black matrix BM having the certain length D is formed and covers an opening through which light from a backlight (not shown) passes, causing a reduction in a transmittance of a liquid crystal panel.